package DoExercise.HSP_ZCY.A006_链表;

import java.util.Stack;

/**
 *
 * 给定一个单链表的头节点head，请判断该链表是否为回文结构
 *
 */
public class Code09_链表是否为回文结构
{
    public static class Node
    {
        public int value;
        public Node next;
        
        public Node(int data)
        {
            this.value = data;
        }
    }
    
    public static boolean isPalindrome1(Node head)
    {
        Stack<Node> stack = new Stack<Node>();
        Node cur = head;
        while (cur != null)
        {
            stack.push(cur);
            cur = cur.next;
        }
        while (head != null)
        {
            if (head.value != stack.pop().value)
            {
                return false;
            }
            head = head.next;
        }
        return true;
    }
    
    //放一半到栈中
    public static boolean isPalindrome2(Node head)
    {
        if (head == null || head.next == null)
        {
            return true;
        }
        Node right = head.next;
        Node cur = head;
        while (cur.next != null && cur.next.next != null)
        {
            right = right.next;
            cur = cur.next.next;
        }
        Stack<Node> stack = new Stack<Node>();
        while (right != null)
        {
            stack.push(right);
            right = right.next;
        }
        while (!stack.isEmpty())
        {
            if (head.value != stack.pop().value)
            {
                return false;
            }
            head = head.next;
        }
        return true;
    }
    
    
    /**
     *
     * 不用容器
     *
     * @param head
     * @return
     */
    public static boolean isPalindrome3(Node head)
    {
        if (head == null || head.next == null)
        {
            return true;
        }
        Node n1 = head;
        Node n2 = head;
        while (n2.next != null && n2.next.next != null)
        {
            n1 = n1.next;
            n2 = n2.next.next;
        }
        //右一半的指针调换顺序
        n2 = n1.next;
        n1.next = null;
        Node n3 = null;
        while (n2 != null)
        {
            n3 = n2.next;
            n2.next = n1;
            n1 = n2;
            n2 = n3;
        }
        n3 = n1;
        n2 = head;
        boolean res = true;
        while (n1 != null && n2 != null)
        {
            if (n1.value != n2.value)
            {
                res = false;
                break;
            }
            n1 = n1.next;
            n2 = n2.next;
        }
        //调回来
        n1 = n3.next;
        n3.next = null;
        while (n1 != null)
        {
            n2 = n1.next;
            n1.next = n3;
            n3 = n1;
            n1 = n2;
        }
        return res;
    }
    
    public static void printLinkedList(Node node)
    {
        System.out.print("Linked List: ");
        while (node != null)
        {
            System.out.print(node.value + " ");
            node = node.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args)
    {
        
        Node head = null;
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(2);
        head.next.next.next = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
        
        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(2);
        head.next.next.next.next = new Node(1);
        printLinkedList(head);
        System.out.print(isPalindrome1(head) + " | ");
        System.out.print(isPalindrome2(head) + " | ");
        System.out.println(isPalindrome3(head) + " | ");
        printLinkedList(head);
        System.out.println("=========================");
    }
    
}
